1. Field of the Invention
The present invention relates to a resistor of the type which includes an insulating substrate and a resistor layer formed on the substrate. The present invention also relates to a method of adjusting the resistance of such a resistor.
2. Description of the Related Art
Conventionally, resistors of the above type have been widely used e.g. for manufacturing various kinds of electric appliances. An example of such resistors is shown in FIG. 13 of the accompanying drawings. The conventional device includes a rectangular substrate 20 made of e.g. a ceramic material, an elongated resistor layer 21 formed on the substrate, a pair of terminal electrodes 22, and a protection cover (not shown) for protecting the resistor layer 21 and the terminal electrodes 22. In the resistor layer 21, a trimming groove 23 is formed for adjusting the resistance of the device. The conventional device is mounted on a printed circuit board (not shown) with the terminal electrodes 22 soldered to the wiring pattern of the circuit board.
The trimming groove 23 of the conventional device is provided at a longitudinally central portion of the resistor layer 21. Due to this arrangement, the conventional device has the following disadvantage.
Specifically, the trimming groove 23 causes the central portion of the resistor layer 21 to have a higher resistance than the remaining portions of the resistor layer. Thus, in use, much heat (Joule heat) will be generated at the central portion of the resistor layer 21 other than the remaining portions of the layer. In an extreme case, most of the heat may be generated only at the central portion of the layer 21 ("localization of heat generation"). According to the conventional arrangement, however, the heat at the central portion of the layer 21 cannot be effectively conducted to the wiring pattern of the circuit board via the terminal electrodes 22, since the central portion of the layer 21 is located apart from these terminal electrodes. As a result, Joule heat may build up at the central portion of the resistor layer 21, which is disadvantageous for maintaining the proper function as a resistor.